Mesh networking is a way to route data and instructions between nodes. A node can be any device connected to a computer network. Nodes can be computers, routers, or various other networked devices. On a TCP/IP network, a node is any device with an Internet Protocol (IP) address. Mesh networking allows for continuous connections and reconfiguration around broken or blocked paths by “hopping” from node to node until the destination is reached. Mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops, and they generally are not mobile devices. In a packet-switching network, a hop is the trip a data packet takes from one router or intermediate node in a network to another node in the network. On the Internet (or a network that uses TCP/IP), the number of hops a packet has taken toward its destination (called the “hop count”) is kept in the packet header.
Wireless mesh networks employ intelligent nodes typically including a wireless (e.g., radio) transmitter and receiver, a power source, input devices, sometimes output devices, and an intelligent controller, such as a programmable microprocessor controller with memory. In the past, wireless mesh networks have been developed having configurations or networks for communication that are static, dynamic or a hybrid of static and dynamic. Power for these networks has been supplied either via wires (i.e., the nodes are “plugged in” or externally powered) or from batteries in each node (i.e., the nodes are internally powered). Networks that employ a combination of externally powered nodes and internally powered nodes can be denoted hybrid networks. As the size, power, and cost of the computation and communication requirements of these devices have decreased over time, battery-powered wireless nodes have gotten smaller; yet, the computing demands on the wireless nodes have increased.
Wireless mesh network technology can be used for deploying sensors as nodes in a variety of different environments for monitoring diverse parameters such as, for example, temperature, pressure, particle counts, and humidity. These types of networks can be denoted wireless sensor networks (WSN). Each sensor in a WSN is typically powered by a battery and therefore has a limited energy supply and operational capability. Because the sensors are constantly monitoring the environment and communicating with other nodes, it is important to efficiently manage the power consumed by each sensing device. Further, it is important to monitor the operational status of each of the sensing devices.
Given that many WSN devices are internally-powered (e.g., battery), the overall network lifetime depends on the efficiency with which sensing, computing, and data transmission by the sensors can be achieved. Because the power requirements for wireless communication by the sensors are orders of magnitude higher than the other sensor operations, it is critical that operation of the radios on these devices be managed carefully. This is primarily achieved by turning the radio on (activating the radio) only when devices need to send and/or receive data and efficiently managing the power output of the radios when they are on. The operational lifetime of the network, thus, depends on the ability to effectively manage the operation of the radios in the wireless network nodes.
The network devices in a WSN must efficiently manage the network topology so that network data packets are properly routed to their destination. In order to carry out this task, the WSN network devices must wake up periodically, activate their radios, and listen for a data communication from another network device to determine if any data packet needs to be routed. Most of the battery power in a wireless network device is consumed when the device must wake up more often, turn the radio on, and listen for a data communication from another network device. Thus, the process of data path maintenance and packet routing through wireless devices in a WSN needs to be highly efficient in order to extend the operational lifetime of the network.
Wireless sensor devices typically use a low power radio device to communicate with other network devices. In most cases, before a network device begins the radio transmission of any data packet, the network device senses the environment for radio frequency (RF) signals or noise to determine if there are other data packets being transmitted by other network devices or other RF sources in the environment. In the presence of excessive RF noise or transmission of RF packets by other network devices, the network device may back off (e.g., delay or cancel a wireless data transmission) for a small amount of time to avoid any data packet collisions. Later, the network device will then try to send the data packet again.
In certain environments, an ambient RF noise level exists on the entire RF spectrum on which the network devices of a WSN are attempting to wirelessly communicate. Further, the level of the ambient noise in the environment may change dynamically over time. In these environments, a network device may not be able to transfer any data via a radio transmission because of the disruptive nature of the ambient noise. In other cases, the network device may only be able to transfer data intermittently via a radio transmission. A system and method is needed that will allow wireless network devices to adapt to this ambient noise and operate efficiently.
U.S. Pat. No. 5,515,369 describes a technology for use in a wireless packet communication system having a plurality of nodes, each having a transmitter and a receiver, the receiver at each node is assigned a seed value and is provided with a channel punchout mask. A node uses its seed value and punchout mask to generate a specific randomly ordered channel hopping band plan on which to receive signals. A node transmits its seed value and punchout mask to target nodes with which it wants to establish communication links, and those target nodes each use the seed value and punchout mask to generate the randomly ordered channel hopping band plan for that node. Subsequently, when one of the target nodes wishes to transmit to the node, the target node changes frequency to the frequency of the node according to that node's band plan.
U.S. Pat. No. 6,590,928 describes a wireless network including master and slave units. The master sends a master address and clock to the slaves. Communication is by means of a virtual frequency hopping channel whose hopping sequence is a function of the master address, and whose phase is a function of the master clock. Transmitted inquiry messages solicit slave address and topology information from the slaves, which may be used to generate a configuration tree for determining a route for a connection between the master and slave units.
U.S. Pat. No. 6,480,497 describes a technology for use in a mesh network communication system, where net throughput is optimized on the link between the communicating nodes by dynamically modifying signal characteristics of the signals transmitted between nodes in response to performance metrics which have been determined from analysis at the receivers for the corresponding links. The signal characteristics can be the data rate, modulation type, on-air bandwidth, etc. The performance metrics are calculated based on data-link on-air characteristics of received signals.
U.S. Patent Application No. 20070258508 describes a method and apparatus for communication in a wireless sensor network. In one embodiment, one or more routers in a network may be available for communication with one or more star nodes at a randomized time and/or frequency. A connectivity assessment, which may be performed at several different frequencies and/or times, may be performed to evaluate the quality of communications between devices in the network. Primary and secondary communication relationships may be formed between devices to provide for system redundancy. One or more proxies may be maintained where each proxy includes a status of one or more devices in the network, e.g., one or more star nodes or routers. Proxies may be used to handle information requests and/or status change requests, e.g., a proxy may be requested to change a communication relationship between devices in the network and may generate command signals to cause the corresponding devices to make the change.
Thus, an apparatus and method for adapting wireless sensor network device operation to ambient RF noise are needed.